Liquid crystal displays (LCDs) are used in a wide range of electronic devices and appliances, from small handheld mobile phones all the way up to large-panel TVs. In general, three main types of LCDs exist and each has characteristics that suit different applications. These three LCD types include: transmissive, reflective, and transflective LCDs. Transmissive and transflective LCDs are of particular relevance to the description herein and are described further below.
A transmissive LCD provides high brightness, contrast, and color saturation and is characterized by its use of a backlight (i.e., an internal light source positioned at the back of the LCD) to provide illumination. The backlight in a transmissive display is typically constructed from white light-emitting diodes (LEDs). The power consumption associated with these backlight LEDs can be relatively high because they are often driven with sufficient power to provide enough light output to compete with the strongest ambient light environments that a device may be operated within, such as outdoor environments where sunlight can be strong.
One solution used to combat the issue of high power consumption is the inclusion and positioning of an ambient light sensor on the outer surface of the LCD. The ambient light sensor is used to estimate the ambient light conditions of the environment where the LCD is currently operating, which is then used to adjust the brightness of the backlight LEDs to meet, but not greatly exceed, the brightness required for the ambient light conditions. Although this solution can improve power consumption, the addition of an ambient light sensor adds cost to the display and increases its overall size. In addition, conventional implementations of transmissive displays that utilize ambient light sensors do not take into consideration the amount of light that the display's own screen adds to the estimated ambient light conditions sensed. Therefore, the brightness of the screen is often adjusted to a sub-optimal setting.
A transflective LCD combines both transmissive functions and reflective functions into one display. In dark or low ambient level conditions, the backlight is turned on and the image is primarily displayed in the transmissive mode. In bright ambient light situations, such as under strong sunlight, the reflective mode primarily functions to illuminate the LCD and the backlight may either be turned on to aid the display of an image or turned off to save power. In the reflective mode, the LCD is specifically illuminated by an external light source, which passes through the front of the LCD and is reflected back by an embedded reflector in the back of the LCD. Because a transflective LCD operating in the reflective mode relies on external light to display an image, it has low power consumption and good readability in high ambient light environments.
To estimate current ambient light conditions such that, in brighter environments, the brightness of the backlight can be reduced to allow the reflective mode of a transflective display to take over, an ambient light sensor is typically used. Although this solution can improve power consumption, the addition of an ambient light sensor, as noted above, adds cost to and increases the overall size of the display.
Therefore, what is needed is an apparatus and method for estimating ambient light conditions for an LCD, while at the same time eliminating the need for a traditional ambient light sensor and the drawbacks associated therewith.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.